Lately, since the introduction of the Renewable Energy Sources Act in Germany, grid-connected photovoltaic systems must be fitted with supply counters. They are installed next to the already existing demand counter and measure the amount of electricity supplied to the domestic grid by the solar power source in kilowatt hours (kWh), which are then credited to the system’s operator (the owner of the solar power system) by the grid operator (the local or regional energy provider) in the bill. Operating capacity and efficiency of the photovoltaic system can be regularly checked by reading the supply counter.

The supply counter remains the property of the grid operator who in turn receives a yearly fee of about 25 to 30 €. Costs and the accounting mode are arranged in the supply contract, with which every system operator comes to an agreement with the grid operator. This agreement however does not depend on which supplier the system operator receives his electricity from.